1. Field of Invention
The present invention relates to an exhaust gas recirculation (EGR) system, and more particularly, to a method for diagnosing an EGR system capable of diagnosing a fault of the EGR system without a separate exhaust temperature sensor by monitoring efficiency of an EGR cooler using pressure and temperature values measured in an intake manifold and an EGR line and capable of controlling a fuel amount of an engine by calculating a flow of EGR and a flow of fresh gas, and a method for controlling fuel injection using the same.
2. Description of Related Art
FIG. 1 is a view schematically showing a configuration of an exhaust gas recirculation (EGR) system according to the related art.
Referring to FIG. 1, in the EGR system, a flow of EGR gas has been controlled based on a manifold absolute pressure (MAP) sensor disposed at a rear end of an electronic throttle actuator control (ETC).
However, in the case in which reliability of a signal value of the MAP sensor is low (disturbance, fault, leakage, or the like), calculation for a flow of fresh air introduced into a combustion chamber as well as the control of the flow of EGR is inaccurate, such that stability of combustion may not be satisfied and an ignition time and a valve overlap time may not be controlled.
Therefore, in order to prevent these problems, a mass air flow (MAF) sensor has been mounted at a front end of the ETC to measure an accurate value for an amount of fresh air, thereby making it possible to secure a basic combustion feature regardless of a fault of the MAP sensor. In addition, when the amount of fresh air is measured by the MAF sensor, it is converted into a pressure value and is then compared with a pressure value measured by the MAP sensor, thereby making it possible to accurately control a flow of EGR.
Meanwhile, an ultimate object of an EGR cooler 1 used in the EGR system is as follows. When a temperature of EGR gas is lowered by the EGR cooler 1, the cooled EGR gas is introduced into a combustion chamber to lower a temperature of the combustion chamber, such that a knocking generation region is suppressed to advance an ignition time, thereby improving a torque and fuel efficiency.
That is, a temperature control of the EGR gas in the EGR system is an important item in several views, and the EGR system recently has a configuration in which the temperature of the EGR gas is lowered by the EGR cooler.
Here, the EGR cooler is an on-board diagnostics (OBD) law item. In order to satisfy fault code monitoring for exhaust gas dissatisfaction of US California Air Resources Board (CARB) and Europe on-board diagnostics (EOBD) forced monitoring, a temperature sensor is mounted at a rear end of the EGR cooler, that is, a front end of an EGR valve to measure the temperature of the EGR gas passing through the EGR cooler, thereby monitoring efficiency of the EGR cooler.
However, in the EGR system according to the related art, as described above, the MAF sensor is installed in order to control the amount of fresh air and the exhaust temperature sensor 2 is separately installed in order to monitor the EGR cooler, so that an additional cost is required to mount the MAF sensor and the exhaust temperature sensor. Particularly, the exhaust temperature sensor, which is a relatively expensive component, causes a cost increase.
Meanwhile, according to the related art, Korean Patent Laid-Open Publication No. 10-2006-0069627 entitled “Method for Controlling EGR Cooler” has been disclosed.
However, even in the method disclosed in Korean Patent Laid-Open Publication No. 10-2006-0069627, since the temperature sensor is mounted in the EGR system, a problem that a component cost required to mount the temperature sensor is increased may not be solved.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.